A wireless communication device, of which a cellular radiotelephone portable subscriber unit is a convenient example, provides an appropriate setting for describing the need for the present invention. The small size of portable radiotelephones enables the user to conveniently carry and store the unit virtually anywhere. This portability, however, allows the portable radiotelephone to be placed in locations where foreign objects may come in contact with a user interface mechanism and inadvertently enable or disable control functions of the radiotelephone. Such undesirable actuation of the control functions is likely to engage related functions which reduce the operating life of a storage battery which powers the portable radiotelephone and may inhibit normal operation.
Some manufacturers offer foldable portable radiotelephones having a housing portion 101 hinged to the body portion 103 of the portable radiotelephone 100 as shown in FIG. 1. Operation of such a portable radiotelephone has been described in U.S. patent application No. 267,156 entitled "Multipurpose Hinge Apparatus" filed in behalf of Beutler et. al. and assigned to the assignee of present invention. The housing portion 101 covers the user interface mechanism 105 when the radiotelephone is not in use and exposes the user interface mechanism when the radiotelephone is in use. To use the portable radiotelephone 100, the user opens the hinged housing portion 101, depresses an "on/off" key on the user interface mechanism 105 to turn the radiotelephone "on" and extends the antenna 109 for optimal wireless communication performance. Disposed on a side of the portable radiotelephone 100 are volume control buttons 107 which may adjust the volume of electroacoustic transducers within the portable radiotelephone 100. To store the portable radiotelephone 100, the user retracts the antenna 109, depresses the "on/off" key to turn the radiotelephone "off" and closes the hinged housing portion 101. The housing portion 101, covering the user interface mechanism 105, offers some protection from accidental control function actuation when the portable radiotelephone 100 is not in use.
In addition to the housing portion covering the user interface mechanism, some manufacturers have taken additional steps to disable control functions when the portable radiotelephone is not in use in the event that small objects such as coins or paper clips should become trapped between the housing portion and the user interface mechanism. A hookswitch, integrated within the portable radiotelephone, senses the position of the housing portion relative to the body portion and may enable or disable control functions responsive to the position of the housing portion relative to the body portion. U.S. Pat. No. 4,845,772 entitled "Portable Radiotelephone With Control Switch Disabling", filed in behalf of Metroka et. al. and assigned to the assignee of the present invention describes a portable radiotelephone which disables an on/off switch under the housing portion and transducer volume level controls 107 on the side of the portable radiotelephone when the portable radiotelephone is not in use. U.S. patent application No. 439,993 entitled "Communications Device With Voice Recognition And Moveable Element Control Interface", filed in behalf of Metroka et. al. on Nov. 20, 1989 describes a portable radiotelephone which deactivates a voice recognition circuit and couples electroacoustic transducers to the portable radiotelephone when the portable radiotelephone is not in use. A cordless telephone manufactured by the Panasonic Company distinguished by model number KXT3000 disables the dialling, number recall, and call processing functions when the housing portion covers the dialling keypad.
The position of the housing portion may also be used to enable control functions of the portable radiotelephone. U.S. patent application No. 439,983 entitled "Communications Device With Moveable Element Control Interface", filed in behalf of Metroka et. al. on Nov. 20, 1989 describes a portable radiotelephone which activates illumination of a keypad, enables a display and a hands free function when the housing portion is opened to expose the user interface mechanism.
Priority goals for portable radiotelephone designs include reducing the radiotelephone's cost, weight and thickness. These goals have been accomplished partly by eliminating the housing portion hinged to the body portion of the portable radiotelephone. Consequently, many of the aforementioned advantages offered by sensing the position of the housing portion relative to the body portion are no longer available and the problems that once plagued portable radiotelephones with exposed user interface mechanisms have resurfaced. Additionally, the hookswitch function, previously performed by positioning the hinged housing portion relative to the body portion, now requires a manual keystroke operation. Manufactures have attempted to compensate for the exposed user interface mechanism by positioning the top surface of individual keys flush with the surrounding housing surface of the body portion. Although this approach eliminates accidental actuation of the keys by large objects, small objects approximately the size of a human finger or smaller may still cause accidental actuation. Additionally, some users having large finger tips complain that the flush keys are difficult to use. Furthermore, accidental actuation is much harder to prevent on radiotelephones having a membrane type user interface mechanism wherein the individual keys are relatively flat and joined to one another without a bordering housing portion to isolate and protect each individual key. Accidental actuation of a membrane type user interface mechanism is usually deterred by including a housing portion that is slightly higher than the mechanism's highest surface and bordering the periphery of the entire keypad.
For may situations, of which cellular portable radiotelephones is merely an example, the prior art has not produced an apparatus or method of generating a control signal to meet the difficult requirement of enabling or disabling control functions at the appropriate time, subject to accidental activation via the exposed user interface mechanism, while providing for the advantage of reduced cost, weight and thickness.